This document discusses non-linear optics, which involves the interaction between light and matter at high intensities of light. It can be used to change the color and shape of light beams. Non-linear optics has applications in optical communications, biomedical imaging, and creating very short events. The key elements discussed are non-linear susceptibility, second harmonic generation, third harmonic generation, four-wave mixing, and the optical Kerr effect. Specific non-linear optical materials like crystals and polymers are also mentioned.

1. Group 1
 Group members:
 Aqsa Batool
 Hasna Batool
 Maryam Kosar
 Izma Ahmad
 Aliza Parveen
 Ayesha Tehreem
 Rubab Ajmal
 Amna Zahid
 Momina Zaka

2. Non-linear Optics

3. Non linear optics (Optics of intense light):
 Defination:
• interaction between light and matter
in the presence of high-intensity
• to change its shape in space and time
• allows us to change the color of a light beam
• involves the generation, propagation, and manipulation of light
• basis of many components of optical communications system
• to create the shortest events ever made by humans

4. Response of optical materials
 Classified into two groups
1. Linear
2. Non-linear
 Linear Response:
 Materials do not depend on the intensity of light
 Follow the laws of classical optics.
 proportional to the intensity of the incident light
Examples
 Stress-strain response of a steel rod under tension up to the yield point
 Elastic deformation of a rubber

5. Non-linear Response:
 Those that depend on the intensity of light
 Do not obey the laws of classical optics
 Proportional to the square of the incident light intensity
 Example:
 Stress-strain response of a steel rod beyond the yield point
 Elastoplastic deformation of a ceramic plate
Key elements in non linear optics
 Nonlinear Susceptibility:
 Second-Harmonic Generation (SHG)
 Third-Harmonic Generation (THG)
 Four-Wave Mixing (FWM)
 Optical Kerr Effect (OKE)
 Nonlinear Optical Materials

6.  Nonlinear Susceptibility:
 describes nonlinear effects in materials
 which quantifies the response of a material to the electric field of light
 Second-Harmonic Generation (SHG):
 two photons of the same frequency interact with a material
 generate a new photon with twice the frequency
 Third-Harmonic Generation (THG):
 the interaction of three photons
 generation of a photon with three times the frequency
 Four-Wave Mixing (FWM):
 two or more incident photons interact within a material
 generate new photons with different frequencies
 Optical Kerr Effect (OKE):
 change in refractive index experienced by a material
 due to the presence of an intense light field.

7. Applications
Frequency Conversion
 Optical Switching
 Optical Limiting
Optical Communications
Biomedical Imaging
Phase conjugation
Non-linear microscopy

8.  Nonlinear Optical Materials:
 Materials that lack inversion symmetry
 They allow for efficient interaction with light.
Example:
 Crystals (e.g., lithium niobate),
 polymers

9. Linear optics:
 a sub-field of optics
 includes in most applications of lenses, mirrors, wave plates, diffraction gratings
 Properties:
 If monochromatic light enters an unchanging linear-optical system, the output will be at the same
frequency
 the superposition principle is valid for linear-optical systems.
 Properties are violated in nonlinear optics
 material interactions including absorption and fluorescence
 high-power pulsed lasers
 Examples
 Phase shifters and beam splitters

10. Non-linear polarization:
 depends nonlinearly on the electric field of the light.
 light propagates in a transparent medium (a dielectric)
 its electric field causes electric polarization in the medium
 at low light intensities
 electric polarization is proportional to the electric field strength
Polarizability: A quantum mechanics point of view
 measure of how polarization occur in atom or molecule
 related to the second derivative of the energy with respect to the electric field
 wave function is perturbed by an electric field, and the change in the energy of the system
 the unperturbed excited-states have different electron distributions than the ground-state,